When Old Medicine Goes Bad

Most of us have reached for a painkiller, at one time or another, only to discover the date on the label shows it's expired. But what does an "expiration" date on medicine really mean? Is it dangerous if you take it anyway? Less effective?

It turns out that date stamped on the label actually means a lot. It's based on scientific evidence gathered by the manufacturer showing how long the drug's potency lasts. Companies expose their medications to different environments, different temperatures and humidity levels to see just how long it takes for the medication to degrade to the point that its effectiveness is compromised.

The general rule, says pharmacist Mike Fossler, with the American College of Clinical Pharmacology, is that once a drug is degraded by 10 percent it has reached "the end of its useful life." If you take it months or even years past the expiration date, it's unlikely to do you any harm, he says; it just might not do you much good.

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